Superconductors are known to include a superconductor made of a simple metal, a superconductor made of a compound, and a superconductor made of composite oxides.
A simple metal superconductor may contain a simple metal such as Pb and Nb but is known to lack utility because it is low in superconducting transition temperature.
Known as intermetallic compound superconductors include those having a Al5 type crystallographic structure of intermetallic compounds as represented by Nb3Ge, Nb3Ga, Nb3Al and Nb3Sn, and those having a chevrel type crystallographic structure of intermetallic compounds as represented by PbMo6S8. Intermetallic compound superconductors having an AlB2 type crystallographic structure of intermetallic compounds as represented by NbB2 are also known which, however, are also known to be extremely low in superconducting transition temperature (Tc=0.62 K, see Journal of the Less-Common Metals, 67 (1979), 249-255). These intermetallic compound superconductors include one with Nb3Ge which is relatively high in superconducting transition temperature (=about 23 K), but commonly have the disadvantage that they are weak in distortion and are fragile.
Known as a composite oxide superconductor include La group oxide superconductors as represented by composition La2−xBaxCuO4, Y group oxide superconductors as represented by composition Y1Ba2Cu3O7−x, Bi group oxide superconductors as represented by composition Bi2Sr2Can−1CunO2n+2, Tl group superconductors as represented by composition Tl2Ba2Can−1CunO2n+2, and Hg group oxide superconductors as represented by Hg1Ba1CaCu1O6+x. These composite oxide superconductors are high in superconducting transition temperature and indeed include those which have their superconducting transition temperatures reaching as high as 150 K. The composite oxide superconductor has a perovskite structure made up of a lamination of an octahedral, pyramidal or planar superconducting layer of CuO2, and a block layer (dissimilar in crystallographic structure to the superconducting layer) made of an atom or atoms such as La, Ca, Y, Bi or Hg and oxygen. As such the extreme complexity of the crystallographic structure of a composite oxide superconductor makes it difficult to conduct its production in a large volume and with good reproducibly. In addition, the superconductor being a composite oxide is naturally poor in both malleability and ductility, and is hard to use as a superconducting electric cable or wire.
A well known alloy superconductor is a Nb—Ti alloy, which is excellent in malleability and ductility and hence has been used to form superconducting electric cables or wires and superconducting magnets. However, an alloy conductor is as low in superconducting transition temperature as, e.g., about 9 K with the Nb—Ti alloy, and hence improvements in them are being sought.
As to superconducting cables or wires, it should also be noted that it may happen that a portion of a superconducting cable incidentally becomes normally conductive. Once this takes place, it may bring about a phenomenon, known as the “quenching” phenomenon, that triggered by Joule heating of the portion rendered normally conductive to have a finite electrical resistance, the entire material in a moment becomes normally conductive. When the quenching phenomenon occurs, serious consequences are met such as the burning of the superconducting cable and the explosive vaporization of coolant, both due to the Joule heat.
An attempt that has so far been made to avoid the quenching phenomenon is to provide a current bypass for a superconducting cable by winding a metal wire low in electric resistivity (specific resistance) around the superconducting cable so that when a portion of the superconducting cables incidentally becomes normally conductive, the current is allowed to escape through the current bypass.
The metal wire low in electric resistivity must, however, be formed of a metal such as silver (Ag) that is expensive and must therefore make the superconducting cable costly.
It is accordingly an object of the present invention to provide an alloy superconductor that is high in superconducting transition temperature and also excels in malleability and ductility, and that can be used to form a superconducting cable without the need for a current bypassing metal wire. It is further an object of the present invention to provide methods of making superconductors reproducibly and at a relative low cost of manufacture.